The headstock holds the spindle and drive mechanism for
turning the work piece. The spindle is a precision shaft and bearing
arrangement rotated directly by a motor or through a motor-driven belt.
Gears or sliding pulleys mounted at the rear of the headstock allow
spindle speed adjustment.
A work piece is held in the spindle for turning or drilling by a jawed
chuck or a spring collet system. Large, unusual shaped, or otherwise
difficult to hold pieces, can be attached to the spindle with a face
plate, drive dogs and special clamps.
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The tailstock supports long work that would otherwise sag or
flex too much to allow for accurate machining. Without a tailstock,
long pieces cannot be turned straight and will invariably have a taper.
Some tailstocks can be intentionally misaligned to accurately cut a
taper if needed. The tailstock has a centering device pressed into a
shallow, specially drilled hole in the end of the work piece. The center
can be either "live" or "dead." Live centers have a bearing, allowing
the center to rotate along with the work piece. Dead centers do not
rotate and must be lubricated to prevent overheating due to friction
with the work piece. Instead of a center, a drill chuck can be mounted
in the tailstock.
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The carriage provides mounting and motion control components
for tooling. The carriage moves left and right, either through manual
operation of a hand wheel, or it can be driven by a lead screw. At the
base of a carriage is a saddle that mates and aligns with the bed ways.
The cross-slide, compound rest and tool holder are mounted to the top of
the carriage. Some carriages are equipped with a rotating turret to
allow a variety of tools to be used in succession for multi-step
operations.
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The cross-slide is mounted to the top of the carriage to
provide movement perpendicular to the length of the bed for facing cuts.
An additional motion assembly, the compound rest, with an adjustable
angle, is often added to the top of the cross slide for angular cuts.
The cutting tools that do the actual metal removal during turning are
mounted in an adjustable tool holder clamped to the compound rest.
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The lead screw provides automatic feed and makes thread
cutting possible. It is a precision-threaded shaft, driven by gears as
the headstock turns. It passes through the front of the carriage apron
and is supported at the tailstock end by a bearing bracket. Controls in
the apron engage a lead nut to drive the carriage as the lead screw
turns.
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